1. Field of the Invention
This invention relates to hybrid vehicles which use electric motors powered by batteries in combination with internal combustion engines to improve fuel efficiency.
2. Description of the Prior Art
There is considerable interest in the development of hybrid vehicles to improve fuel efficiency without sacrifice in mechanical performance. Such vehicles combine the use of internal combustion engines and electric motors.
Some hybrid vehicles use a relatively small but fuel-efficient internal combustion engine to enable it to cruise economically, and use additional power from the electric motor to assist in acceleration and hill-climbing, etc. Others use the electric motor to cruise, and supplement it with power from the engine for acceleration and hill-climbing, etc. Still others use any combination of both modes of operation. Power from the engine is used to charge the batteries. Regenerative braking is sometimes used to assist in recharging the batteries and thereby conserve fuel.
Although the hybrid system significantly improves automotive fuel efficiency, it has many disadvantages. It often requires severe down-sizing of the engine to achieve improved fuel efficiency and therefore needs a powerful electric motor to add sufficient power for acceleration and hill-climbing. This requires a complex and expensive electrical control system, a set of high capacity, high output batteries, and a powerful electric motor, resulting in high initial cost and high maintenance costs. These costs may not be fully offset by savings attributable to the improved fuel efficiency of the vehicle. For instance, the limited useful life of the batteries will require them to be replaced before these savings are fully realized.
On the other hand, using a large engine in combination with a smaller, less powerful but less expensive electric motor system will not solve the problem either. Firstly, the larger engine will be less fuel-efficient because of its larger size. Then, to cruise economically the vehicle will still need a sufficiently powerful electric motor with high capacity powerful batteries to supply enough power for cruising, otherwise the larger engine will have to be operated more, simply to assist in cruising. This would reduce the vehicle's fuel efficiency, yet still largely retain the high initial and maintenance cost of the components of the system.
So far, therefore, the hybrid vehicle as an approach towards achieving fuel efficiency in motor vehicles is proving to be unsatisfactory. If the engine is downsized sufficiently to permit the vehicle to cruise economically, the electric motor has to be made powerful enough to give the vehicle acceptable acceleration and hill climbing capability; but the powerful electric motor is expensive and requires expensive high capacity batteries, resulting in high initial and maintenance cost. On the other hand, if the electric motor is made less powerful so as to reduce its cost and the cost of the batteries, then the engine will need to be more powerful (and less fuel efficient) in order for the vehicle to have acceptable acceleration and hill-climbing capability.
What is needed is a system that will not only permit sufficient downsizing of the engine that is used for cruising so that the vehicle can cruise over long distances with significantly reduced fuel consumption, but will also permit sufficient downsizing of the electric motor and batteries. Such downsizing should be accomplished without sacrifice in the accelerating and hill-climbing performance of the vehicle, and preferably without extensive redesign of motor vehicles as they currently exist.
The prior art has not met this need. The present invention is intended to provide a solution to this problem. It does so by recognizing that motor vehicles really need two distinct types of power sources in order to have satisfactory mechanical performance and to achieve high fuel efficiency for long distance travel. These requirements are, namely, (1) a power source with high power output and high torque for acceptable acceleration, towing and hill-climbing capability, and (2) a lower power output power source capable of providing continuous lower power with high fuel-efficiency for long distance travel at cruising speeds. This invention meets the first requirement through the use of the standard power train of current motor vehicles without any essential modifications, and then meets the second requirement through the use of a fuel-efficient hybrid system comprising a secondary, smaller internal combustion auxiliary engine augmented by an electric motor for cruising. Furthermore mechanical efficiency of this hybrid system is improved by directly coupling the hybrid system to the drive axle, bypassing the transmission, thereby eliminating any frictional power losses generated in the transmission.
The manner of interaction of these various drive components are unobvious and they produce these unexpected advantages. This particular combination of parts and the manner in which they interact to achieve these results has not previously been described.
U.S. Pat. No. 6,179,078 to Belloso discloses an inexpensive, fuel-efficient automobile which uses two internal combustion engines; two for acceleration and one for cruising. Each engine is coupled to a driving wheel via a torque converter. It uses an electric motor for reverse motion, not for the purpose of improving fuel economy.
U.S. Pat. No. 6,852,062 to Abner, et. al., discloses two internal combustion engines and one or two starter/generators, all coupled to one transmission. It uses two engines to start and then uses the engines and motors to individually or jointly transmit power to the transmission thence to the drive wheels of the vehicle. None of the engines or motors bypass the transmission for the purpose of eliminating frictional power losses. The many modifications necessary to couple the two internal combustion engines and starter/generators to the transmission and to coordinate their functions make it difficult to use this system as an add-on feature to currently existing motor vehicles.
U.S. Pat. No. 6,722,458 to Hofbauer discloses two internal combustion engines which are both coupled by clutches to one transmission which drives the drive wheels. It further discloses the use of one or two electric motors. The vehicle starts and accelerates on power from the two engines, possibly supplemented by power from the motor(s), and cruises on power from one engine, one motor or a combination of both. Neither of the engines bypass the transmission for the purpose of eliminating frictional power losses generated therein. It does not teach the specific use of a fuel-efficient engine directly coupled to the differential primarily for the purpose of maintaining the vehicle at cruising speed. The many modifications needed to couple both engines and possibly one electric motor to the transmission and the associated control means to coordinate their function make it difficult to adapt this system as an add-on feature to existing motor vehicles.
U.S. Pat. No. 6,306,056 to Moore discloses a dual engine hybrid electric vehicle including two internal combustion engines and one motor/generator. Both engines are coupled to one transmission which is then coupled to the differential and drive wheels. During normal driving conditions a single engine is used. When load increases, the electric motor is used temporarily, then the second engine is speeded up to assist the first engine. Presumably both engines are used to start and accelerate the vehicle until it reaches normal driving conditions, wherein one engine may be turned off. Neither engine bypasses the transmission for the specific purpose of eliminating any frictional power losses generated therein. The many modifications necessary to couple both engines to a single transmission makes this system unacceptable as an add-on feature for an existing vehicle.
U.S. Pat. No. 5,492,189 to Kriegler, et. al., discloses a hybrid drive system comprising one internal combustion engine operating in steady-state mode and two transiently operating engines configured as hydraulic engines or electric motors. All engines are coupled to a planetary gear system with associated control means for coordinating the functioning of the internal combustion engine and the two transient engines. It does not disclose use of two internal combustion engines. It does not teach use of a primary internal combustion combined with a secondary internal combustion engine augmented by an electric motor bypassing the transmission, for the specific purpose of maintaining the vehicle at cruising speed. Furthermore, the many new features and modifications to adapt this system to a planetary gear system precludes easy application as an add-on feature to current motor vehicles.
U.S. Pat. No. 6,814,686 to Carriere, et. al., discloses primary and secondary engines and a phase clutch interactive between the crankshafts of the primary and secondary engines to provide proper coupling of the crankshafts. Both engines are coupled to one transmission which transmits power to drive the vehicle. Both engines are used to start and accelerate, and one engine is used to cruise.
It is accordingly an object of this invention to provide a hybrid vehicle capable of traveling at cruising speed for long distances with improved fuel efficiency.
It is another object of the present invention to provide a vehicle as in the foregoing object which does not require expensive powerful electric motors and powerful high-capacity batteries.
It is a further object of this invention to provide a vehicle of the aforesaid nature having sufficient power for quick acceleration and good hill-climbing abilities.
It is a still further object of the present invention to provide a component system for enhancing the fuel efficiency of motor vehicles, said system being amenable to installation into current motor vehicles in the streets and preserving the integrity of the power train of these vehicles.
It is yet another object of this invention to provide a hybrid vehicle with improved fuel efficiency and reduced manufacturing and maintenance costs.
These objects and other objects and advantages of the invention will be apparent from the following description.